Ask a Master Gardener with Marianne Mueller – Downy Skullcap

Ask a Master Gardener with Marianne Mueller – Downy Skullcap

Arlyn introduced Hoary Skullcap to the greenhouse this spring. Its name sounded like some kind of Halloween freak show to me, and I decided that I would wait a year, see if it bloomed, and check out what it looked like before promoting the plant. So, I would look skeptically at the flat when in its neighborhood. In mid-summer, much to my surprise, I thought I saw some buds forming toward the tops of the stems – sure enough, unlike many perennial plants, this one was going to bloom the first year from seed! A good sign, but I was still going to reserve judgment until the buds opened, and I could really see what it was going to do – I mean, seriously, with a name like Hoary Skullcap, how much can a person expect? What I learned was a variation on a theme that I constantly remind my students of…you don’t judge a book by its cover, and likewise, I mustn’t judge a wildflower by its name! 

This perennial member of the mint family will grow 2-3 feet tall, with few branches, except near the top.  The central stem is strongly erect, whitish green, bluntly square, and covered with short, fine hair. Leaves are opposite on the stem, about 3” long and 1 ½” wide, lance shaped with bluntly toothed edges.  The top of the leaf is pale to medium or yellowish green and pretty much smooth while the underside is whitish green and covered with the same fine, short hair as the stem.  The plant will begin to bloom in mid-late summer and will continue blooming for a month to a month and a half. A flower spike up to 6” long forms at the tops of the square stems. These upright spikes are densely packed with pairs of flowers. Each flower has a two-lipped tubular blossom about ¾” long rising from a short tubular base.  The upper lip is hood-like with edges that are curled back, while the lower lip is broader and quite a bit larger. The color will range from deep to light purple, with a conspicuous patch of white nestled in at the throat of the lower lip.  Very fine hair covers the outer surface of each flower, not sticky, but soft and downy.  As almost the entire plant (with the exception of the upper leaf surface) is covered with this soft, short hair, it is also known as …wait for it… Downy Skullcap. In fall, the blooms are replaced with whimsical purplish red seedpods; each pod will contain 2-4 nutlets. The root system contains rhizomes, and may form tight colonies of plants.

Downy Skullcap prefers part shade but will do fine in a full range of light conditions from full sun to deep shade. It is also accommodating as to soil; it prefers slightly acidic conditions, does best in dryish sandy or clay soils, but is easily grown in average, dry to medium, well-drained soil. The plant is pollinated primarily by bumblebees, which suck nectar or collect pollen. The foliage is bitter-tasting and possibly toxic, so deer don’t bother it to any significant degree.

I am changing my plant tags to read Downy Skullcap, a name more suited to this elegant, showy plant of refined growth and leafage.  It’s good in wildflower gardens, native plant gardens, open woodland areas, or perennial borders. Looking somewhat like a restrained version of foxglove, Downy Skullcap can be a highly ornamental, interesting and attractive addition to your flower pallet.


Marianne Mueller, Master Gardener, M&M Greenhouse, Barnes, WI.  Please continue to send your questions to Please reference “MG” in the subject line to foil the junk mail filter swallowing it! We will get to all your questions in future issues.